Messages in this thread | | | Date | Mon, 14 Mar 2022 12:17:29 +0530 | Subject | Re: [RFC V1 11/11] perf: Capture branch privilege information | From | Anshuman Khandual <> |
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On 1/26/22 22:57, James Clark wrote: > > On 24/01/2022 04:30, Anshuman Khandual wrote: >> Platforms like arm64 could capture privilege level information for all the >> branch records. Hence this adds a new element in the struct branch_entry to >> record the privilege level information, which could be requested through a >> new event.attr.branch_sample_type flag PERF_SAMPLE_BRANCH_PRIV_SAVE. While >> here, update the BRBE driver as required. >> >> Cc: Will Deacon <will@kernel.org> >> Cc: Mark Rutland <mark.rutland@arm.com> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Ingo Molnar <mingo@redhat.com> >> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> >> Cc: Jiri Olsa <jolsa@redhat.com> >> Cc: Namhyung Kim <namhyung@kernel.org> >> Cc: linux-arm-kernel@lists.infradead.org >> Cc: linux-perf-users@vger.kernel.org >> Cc: linux-kernel@vger.kernel.org >> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> >> --- >> drivers/perf/arm_pmu_brbe.c | 28 ++++++++++++++++++++++++ >> include/linux/perf_event.h | 5 +++++ >> include/uapi/linux/perf_event.h | 13 ++++++++++- >> tools/include/uapi/linux/perf_event.h | 13 ++++++++++- >> tools/perf/Documentation/perf-record.txt | 1 + >> tools/perf/util/parse-branch-options.c | 1 + >> 6 files changed, 59 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/perf/arm_pmu_brbe.c b/drivers/perf/arm_pmu_brbe.c >> index 7cd1208c6c58..d4cbea74c148 100644 >> --- a/drivers/perf/arm_pmu_brbe.c >> +++ b/drivers/perf/arm_pmu_brbe.c >> @@ -270,6 +270,25 @@ static int brbe_fetch_perf_type(u64 brbinf) >> } >> } >> >> +static int brbe_fetch_perf_priv(u64 brbinf) >> +{ >> + int brbe_el = brbe_fetch_el(brbinf); >> + >> + switch (brbe_el) { >> + case BRBINF_EL_EL0: >> + return PERF_BR_USER; >> + case BRBINF_EL_EL1: >> + return PERF_BR_KERNEL; >> + case BRBINF_EL_EL2: >> + if (is_kernel_in_hyp_mode()) >> + return PERF_BR_KERNEL; >> + return PERF_BR_HV; >> + default: >> + pr_warn("unknown branch privilege captured\n"); >> + return -1; >> + } >> +} >> + >> static void capture_brbe_flags(struct pmu_hw_events *cpuc, struct perf_event *event, >> u64 brbinf, int idx) >> { >> @@ -302,6 +321,15 @@ static void capture_brbe_flags(struct pmu_hw_events *cpuc, struct perf_event *ev >> cpuc->brbe_entries[idx].in_tx = brbinf & BRBINF_TX; >> } >> } >> + >> + if (branch_sample_priv(event)) { >> + /* >> + * All these information (i.e branch privilege level) are not >> + * available for source only branch records. >> + */ >> + if (type != BRBINF_VALID_SOURCE) >> + cpuc->brbe_entries[idx].priv = brbe_fetch_perf_priv(brbinf); >> + } >> } >> >> /* >> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h >> index 916ce5102b33..8021b6a30d86 100644 >> --- a/include/linux/perf_event.h >> +++ b/include/linux/perf_event.h >> @@ -1688,4 +1688,9 @@ static inline bool branch_sample_hw_index(const struct perf_event *event) >> { >> return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_HW_INDEX; >> } >> + >> +static inline bool branch_sample_priv(const struct perf_event *event) >> +{ >> + return event->attr.branch_sample_type & PERF_SAMPLE_BRANCH_PRIV_SAVE; >> +} >> #endif /* _LINUX_PERF_EVENT_H */ >> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h >> index 361fdc6b87a0..4d77710f7a4e 100644 >> --- a/include/uapi/linux/perf_event.h >> +++ b/include/uapi/linux/perf_event.h >> @@ -204,6 +204,8 @@ enum perf_branch_sample_type_shift { >> >> PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT = 17, /* save low level index of raw branch records */ >> >> + PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT = 18, /* save privillege mode */ >> + >> PERF_SAMPLE_BRANCH_MAX_SHIFT /* non-ABI */ >> }; >> >> @@ -233,6 +235,8 @@ enum perf_branch_sample_type { >> >> PERF_SAMPLE_BRANCH_HW_INDEX = 1U << PERF_SAMPLE_BRANCH_HW_INDEX_SHIFT, >> >> + PERF_SAMPLE_BRANCH_PRIV_SAVE = 1U << PERF_SAMPLE_BRANCH_PRIV_SAVE_SHIFT, >> + >> PERF_SAMPLE_BRANCH_MAX = 1U << PERF_SAMPLE_BRANCH_MAX_SHIFT, >> }; >> >> @@ -265,6 +269,12 @@ enum { >> PERF_BR_MAX, >> }; >> >> +enum { >> + PERF_BR_USER = 0, >> + PERF_BR_KERNEL = 1, >> + PERF_BR_HV = 2, >> +}; >> + > Can we have 0 as "UNKNOWN". It's going to be difficult to parse files when privilege information > isn't saved and get accurate results without that. For example if it's not set then presumably > the field would be 0 (PERF_BR_USER), but that doesn't mean the samples are user in that case. > > I know you might be able to go backwards and look at what arguments were passed to the kernel but > it's not guaranteed that the kernel honored the request anyway. There are also other platforms > to think about etc. > > If you look at the branch type definitions above they start at 0 (PERF_BR_UNKNOWN) which I think > works out quite nicely in the userspace code.
This is being taken care in the new BRBE related perf ABI changes series (V3).
https://lore.kernel.org/all/20220314055857.125421-1-anshuman.khandual@arm.com/
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